1. Field of the Invention
The present invention relates generally to ink jet printing apparatus, and more particularly relates to the fabrication of piezoelectrically operable ink jet printhead assemblies.
2. Description of Related Art
A piezoelectrically actuated ink jet printhead is a device used to selectively eject tiny ink droplets onto a print medium sheet operatively fed through a printer, in which the printhead is incorporated, to thereby form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has, within its body portion an internal array of horizontally spaced, mutually parallel ink receiving channels. These internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric wall portions of the printhead body (typically formed from a piezoceramic material referred to as "PZT") separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice.
A conventional method of fabricating an ink jet printhead of this type has been to provide top and bottom rectangular blocks of appropriately polled PZT material respectively having bottom and top side surfaces and front and rear ends, with the bottom PZT block having a longer front-to-rear length than the top PZT block. A recessed ink supply header is appropriately formed in the bottom side surface of the top PZT block adjacent its rear end.
To provide for the proper transmission of electrical driving signals to the interior of the finished printhead body, the bottom and top side surfaces of the top and bottom PZT blocks, respectively must be laboriously metallized before forming the interior body channels and attaching the front end orifice plate. Typically, the metallizing coating applied to these printhead body surfaces comprises a layer of a Ni/Cr coating to the outer side surface of which a layer of gold is applied to provide satisfactory electrical conductivity characteristics to the finished metallization coating.
After the metallization coating is applied to these surfaces of the top and bottom PZT body blocks, spaced series of grooves that extend between the front and rear ends of the blocks are cut (using a precision dicing saw) through the metallization coatings and into the underlying PZT material, with rear end portions of the grooves in the top PZT block communicating with its ink supply header. Using an appropriate electrically conductive adhesive material, the metallized coatings are then bonded together, with the front ends of the top and bottom blocks, and their side surface grooves, being precisely aligned with one another.
In this partially assembled state of the printhead body, the aligned grooves form the interior ink receiving channels within the printhead body, and a rear end portion of the bottom PZT block and its grooves extend rearwardly beyond the rear end of the top PZT block. Both the front ends and the rear ends of the channels are open at this point in the fabrication process.
To complete the fabrication of the printhead the orifice plate is operatively positioned on and secured to the front end of the body and the rear end of the ink receiving channels are appropriately sealed off. Additionally, an ink supply tube is suitably communicated with the interior ink supply header. On the exposed rear top side portion of the bottom PZT block, the grooves formed therein form a spaced series of exposed, ribs in the bottom block with the top sides of these ribs being covered with remaining strips of the metallization coating originally applied to the top side surface of the bottom PZT block.
These top side metal strips are used as electrically conductive traces through which piezoelectric driving signals may be transmitted to the spaced series of channel side walls defined within the interior of the printhead body by the metallized, bonded together groove ribs therein. These sidewall deflecting driving signals are transmitted to the interior of the printhead body via the electrically conductive surface traces on a flexible ribbon cable connected at one end to the exposed metallized surface strips on the lower PZT block, and at the other end to an appropriate electronic driver device external to the printhead.
This conventional piezoelectric ink jet printhead fabrication technique has two primary disadvantages. First, as is well known, the metallization of the opposing PZT body portion surfaces is a tedious, time-consuming, relatively expensive task that must be very carefully performed to achieve satisfactory printhead performance. Additionally, the relatively thin ribs extending along the exposed rear end portion of the bottom PZT block are susceptible to breakage, thereby potentially leading to disruption of the critical piezoelectrical driving circuitry.
It can be seen from the foregoing that it would be desirable to provide improved piezoelectric ink jet printhead apparatus, and associated fabrication methods, that eliminate or at least substantially reduce one or more of the foregoing problems, limitations and disadvantages associated with ink jet printheads conventionally constructed as generally described above. It is accordingly an object of the present invention to provide such improved ink jet printhead apparatus and associated fabrication methods.